prta-20260327

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

____________________

SCHEDULE 14A

Proxy Statement Pursuant to Section 14(a) of the

Securities Exchange Act of 1934

____________________

Filed by the Registrant

☒

Filed by a Party other than the Registrant

☐

Check the appropriate box:


☐			Preliminary Proxy Statement


☐			Confidential, for Use of the Commission Only (as permitted by Rule 14a-6(e)(2))


☒			Definitive Proxy Statement


☐			Definitive Additional Materials


☐			Soliciting Material Pursuant to § 240.14a-12

____________________

PROTHENA CORPORATION PUBLIC LIMITED COMPANY

(Name of registrant as specified in its charter)

____________________

(Name of Person(s) Filing Proxy Statement, if other than the Registrant)

Payment of Filing Fee (Check all boxes that apply):


☒						No fee required.

☐						Fee paid previously with preliminary materials.

☐						Fee computed on table in exhibit required by Item 25(b) per Exchange Act Rules 14a-6(i)(1) and 0-11

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PROTHENA CORPORATION PLC

Registered in Ireland - No. 518146

77 Sir John Rogerson’s Quay, Block C, Grand Canal

Docklands, Dublin 2, D02 VK60, Ireland

NOTICE OF ANNUAL GENERAL MEETING OF

SHAREHOLDERS TO BE HELD ON MAY 14, 2026

To the Shareholders of Prothena Corporation plc:

NOTICE IS HEREBY GIVEN that the Annual General Meeting of Shareholders (the “Annual Meeting”) of Prothena Corporation plc, an Irish public limited company (the “Company”), will be held on Thursday, May 14, 2026, at 4:00 p.m. local time, at The Merrion Hotel, Upper Merrion Street, Dublin 2, D02 KF79, Ireland for the following purposes:

1.To elect, by separate resolutions, Shane M. Cooke and Dennis J. Selkoe, as directors, to hold office until no later than the annual general meeting of shareholders in 2029;

2.To ratify, in a non-binding vote, the appointment of KPMG LLP as the Company’s independent registered public accounting firm for its fiscal year ending December 31, 2026, and to authorize, in a binding vote, the Company’s Board of Directors, acting through its Audit Committee, to approve the remuneration of that auditor;

3.To approve, in a non-binding advisory vote, the compensation of the Company’s executive officers named in the Proxy Statement accompanying this Notice; and

4.To transact such other business as properly comes before the Annual Meeting or any adjournment or postponement thereof.

The foregoing items of business are more fully described in the Proxy Statement accompanying this Notice. The Company’s Irish statutory financial statements for its fiscal year 2025, including the reports of the directors and auditors thereon, will be presented at the Annual Meeting. There is no requirement under Irish law that those statutory financial statements be approved by shareholders and no such approval will be sought at the Annual Meeting. The Annual Meeting will also include a review of the Company’s affairs.

Under our Constitution and Irish law, Proposal Nos. 1, 2, and 3 are deemed to be ordinary resolutions requiring the approval of a simple majority of the votes cast at the Annual Meeting.

Only shareholders who owned our ordinary shares at the close of business on March 2, 2026, may vote at the Annual Meeting. Each shareholder of record will be entitled to one vote per ordinary share on each matter submitted to a vote of the shareholders, as long as those shares are represented at the Annual Meeting, either in person or by proxy. Shareholders who are entitled to attend and vote at the Annual Meeting are entitled to appoint a proxy or proxies to attend and vote on their behalf at the Annual Meeting; such proxy is not required to be a shareholder of the Company.

Our Board of Directors unanimously recommends that you vote as follows on the matters to be presented to shareholders at the Annual Meeting:

1.FOR the election of Shane M. Cooke and Dennis J. Selkoe, as directors, as described in Proposal No. 1;

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2.FOR the ratification, in a non-binding vote, of the appointment of KPMG LLP as the Company’s independent registered public accounting firm for its fiscal year 2026, and authorization, in a binding vote, of the Board of Directors, acting through its Audit Committee, to approve the remuneration of that auditor, as described in Proposal No. 2; and

3.FOR the approval, in a non-binding advisory vote, of the compensation of the Company’s named executive officers, as described in Proposal No. 3.

For the Annual Meeting, we have elected to use the internet as the primary means of providing our proxy materials to shareholders. Consequently, some shareholders may not receive paper copies of our proxy materials. We intend to send shareholders a Notice of Internet Availability of Proxy Materials with instructions for accessing the proxy materials and for voting via the internet. The Notice of Internet Availability of Proxy Materials will also provide the date, time, and location of the Annual Meeting; the matters to be acted upon at the meeting and the Board of Directors’ recommendation with regard to each matter; a toll-free number, an e-mail address, and a website where shareholders can request a paper or e-mail copy of our Proxy Statement and form of proxy card and our Annual Report on Form 10-K for fiscal year 2025; information on how to access their proxy card; and information on how to attend the meeting and vote in person.

You are cordially invited to attend the Annual Meeting, but whether or not you expect to attend in person, you are urged to complete, sign, and date your proxy card and return it by mail or follow the alternative voting procedures described in the Notice of Internet Availability of Proxy Materials or the proxy card.


			By Order of the Board of Directors



			Michael J. Malecek
			Company Secretary
			Dublin, Ireland
			March 27, 2026

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			Page
GENERAL INFORMATION			1
THE PROXY PROCESS AND SHAREHOLDER VOTING - QUESTIONS AND ANSWERS ABOUT THESE PROXY MATERIALS AND VOTING			2
PROPOSAL NO. 1 - ELECTION OF DIRECTORS			7
CORPORATE GOVERNANCE AND BOARD MATTERS			12
Overview			12
Independence of Directors			12
Board Role in Risk Oversight			12
Board Leadership Structure			12
Board Committees			12
Audit Committee			13
Compensation Committee			13
Nominating and Corporate Governance Committee			14
Research and Development Committee			15
Meetings of the Board and Committees, Meeting Attendance, and Shareholder Meeting Attendance			15
Other Corporate Governance Matters			15
DIRECTOR COMPENSATION - FISCAL YEAR 2025			16
PROPOSAL NO. 2 - APPOINTMENT OF KPMG LLP AS OUR INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM			19
Fees Paid to KPMG			19
Pre-Approval Policies and Procedures			20
REPORT OF THE AUDIT COMMITTEE OF THE BOARD OF DIRECTORS			20
PROPOSAL NO. 3 - SAY-ON-PAY VOTE			21
SECURITY OWNERSHIP OF CERTAIN BENEFICIAL OWNERS AND MANAGEMENT			23


			Page
COMPENSATION DISCUSSION AND ANALYSIS			25
Executive Summary: Fiscal Year 2025 Company Performance and Key Pay Decisions			25
Compensation Governance and Best Practices			28
Shareholder Approval of Executive Compensation			28
The Objective of Our Executive Compensation Programs			29
How We Determine Executive Compensation			29
Executive Compensation for Fiscal Year 2025			31
Employment and Severance Arrangements			34
REPORT OF THE COMPENSATION COMMITTEE OF THE BOARD OF DIRECTORS			34
EXECUTIVE COMPENSATION			36
Summary Compensation Table - Fiscal Year 2025			36
Grants of Plan-Based Awards - Fiscal Year 2025			37
Outstanding Equity Awards at Fiscal Year-End - Fiscal Year 2025			38
Option Exercises and Stock Vested - Fiscal Year 2025			40
Potential Payments and Benefits upon Termination of Employment			41
Change in Control and Severance Arrangements			42
Compensation Risk Assessment			46
Pay Ratio of Chief Executive Officer to Median Employee			46
Pay Versus Performance			47
Policies and Practices Related to the Timing of Grants of Certain Awards			51
EQUITY COMPENSATION PLAN INFORMATION			52
TRANSACTIONS WITH RELATED PERSONS AND INDEMNIFICATION			53
HOUSEHOLDING OF PROXY MATERIALS			54
ANNUAL REPORT			54

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PROTHENA CORPORATION PLC

Registered in Ireland - No. 518146

77 Sir John Rogerson’s Quay, Block C, Grand Canal

Docklands, Dublin 2, D02 VK60, Ireland

PROXY STATEMENT

FOR THE ANNUAL GENERAL

MEETING OF SHAREHOLDERS

TO BE HELD ON MAY 14, 2026

GENERAL INFORMATION

The Board of Directors of Prothena Corporation plc is soliciting your proxy to vote at the Annual General Meeting of Shareholders to be held on Thursday, May 14, 2026, at 4:00 p.m. local time, and any adjournment or postponement of that meeting (the “Annual Meeting”). The Annual Meeting will be held at The Merrion Hotel, Upper Merrion Street, Dublin 2, D02 KF79, Ireland.

We have elected to use the internet as our primary means of providing our proxy materials to shareholders. Accordingly, on or about March 27, 2026, we are making this Proxy Statement and the accompanying form of proxy card, the accompanying Notice of Annual General Meeting of Shareholders, and our Annual Report on Form 10-K for our fiscal year 2025 available on the internet and mailing a Notice of Internet Availability of Proxy Materials to shareholders of record as of close of business on March 2, 2026 (the “Record Date”). Brokers and other nominees who hold shares on behalf of beneficial owners will be sending their own similar notice. All shareholders as of the Record Date will have the ability to access our proxy materials on the website referred to in the Notice of Internet Availability of Proxy Materials or request to receive a printed set of the proxy materials. Instructions on how to request a printed copy by mail or electronically may be found in the Notice of Internet Availability of Proxy Materials and on the website referred to in the notice, including an option to request paper copies on an ongoing basis. We intend to mail this Proxy Statement, together with the accompanying form of proxy card and Notice of Annual General Meeting of Shareholders, to those shareholders entitled to vote at the Annual Meeting who have properly requested paper copies of such materials.

The only voting securities of Prothena are our ordinary shares, $0.01 par value per share (“ordinary shares”). There were 53,832,982 ordinary shares issued and outstanding as of the Record Date. A quorum of shareholders is necessary to hold a valid meeting and requires that the shareholders holding a majority of the issued and outstanding ordinary shares entitled to vote are present in person or represented by proxy at the Annual Meeting.

In this Proxy Statement, we refer to Prothena Corporation plc as the “Company,” “Prothena,” “our,” “we,” or “us” and the Board of Directors as the “Board.” When we refer to Prothena's fiscal year, we mean the 12-month period ending December 31 of the stated year. The contents of our website are not intended to be incorporated by reference in this Proxy Statement, and any references to our website herein are intended for textual references only.


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THE PROXY PROCESS AND SHAREHOLDER VOTING QUESTIONS AND ANSWERS ABOUT THESE PROXY MATERIALS AND VOTING


1.			Who can vote at the Annual Meeting?

Only shareholders of record at the close of business on the Record Date will be entitled to vote at the Annual Meeting. As of the Record Date, there were 53,832,982 ordinary shares issued and outstanding and entitled to vote.

Shareholder of Record: Shares Registered in Your Name

If, on the Record Date, your shares were registered directly in your name with the transfer agent for our ordinary shares, Computershare Trust Company, N.A., then you are a shareholder of record. As a shareholder of record, you may vote in person at the Annual Meeting or vote by proxy. Whether or not you plan to attend the Annual Meeting, we urge you to fill out and return the enclosed proxy card or vote by proxy over the telephone or on the internet as instructed below to ensure your vote is counted.

Beneficial Owner: Shares Registered in the Name of a Broker, Bank, or Other Agent

If, on the Record Date, your shares were not held in your name, but rather in an account at a brokerage firm, bank, dealer, or other similar organization, who in turn hold through The Depository Trust Company (“DTC”), then you are the beneficial owner of shares held in “street name” and these proxy materials are being forwarded to you by that organization. The organization holding your account is considered the shareholder of record for purposes of voting at the Annual Meeting. As a beneficial owner, you have the right to direct your broker or other agent on how to vote the shares in your account. You are also invited to attend the Annual Meeting. However, since you are not the shareholder of record, you may not vote your shares in person at the Annual Meeting unless you request and obtain a valid proxy card from your broker or other agent who is the record holder of the shares, authorizing you to vote at the Annual Meeting.


2.			What am I being asked to vote on?

You are being asked to vote FOR:

•Election, by separate resolutions, of Shane M. Cooke and Dennis J. Selkoe as directors, to hold office until no later than our annual general meeting of shareholders in 2029;

•Ratification, in a non-binding vote, of the appointment of KPMG LLP as our independent registered public accounting firm for our fiscal year 2026, and authorization, in a binding vote, of our Board, acting through its Audit Committee, to approve the remuneration of that auditor; and

•Approval, in a non-binding advisory vote, of the compensation of our executive officers named in this Proxy Statement.

In addition, you are entitled to vote on any other matters that are properly brought before the Annual Meeting. We are not aware of any other matter that will be presented for consideration at the Annual Meeting. If any other matter is properly brought before the Annual Meeting, the Board intends that one of the individuals named in the accompanying form of proxy card will vote on such matter in accordance with his or her discretion.


3.			How do I vote?

You may vote by mail or follow any alternative voting procedure described on the proxy card or the Notice of Internet Availability of Proxy Materials. To use an alternative voting procedure, follow the instructions on each proxy card that you receive or on the Notice of Internet Availability of Proxy Materials.

For Proposals 1, 2, and 3, you may vote “FOR” or “AGAINST” or abstain from voting.

The procedures for voting are as follows:


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			THE PROXY PROCESS AND SHAREHOLDER VOTING
QUESTIONS AND ANSWERS ABOUT THESE PROXY MATERIALS AND VOTING

Shareholder of Record: Shares Registered in Your Name

If you are a shareholder of record, you may vote in person at the Annual Meeting. Alternatively, you may vote by proxy by mail, over the internet, or by telephone. Whether or not you plan to attend the Annual Meeting, we urge you to vote by proxy to ensure your vote is counted. Even if you have submitted a proxy before the Annual Meeting, you may still attend the Annual Meeting and vote in person. In such case, your previously submitted proxy will be disregarded.

•To vote in person, come to the Annual Meeting and we will give you a ballot when you arrive.

•To vote using the proxy card, simply complete, sign, and date the proxy card and return it promptly in the envelope provided. If you return your signed proxy card to us before the Annual Meeting, we will vote your shares as you direct.

•To vote by proxy over the internet, follow the instructions provided on the proxy card or in the Notice of Internet Availability of Proxy Materials.

•To vote by telephone if you request printed copies of the proxy materials by mail, you may vote by proxy by calling the toll-free number found on the proxy card.

Beneficial Owner: Shares Registered in the Name of Broker, Bank, or Other Agent

If you are a beneficial owner of shares registered in the name of your broker, bank, or other agent, who in turn hold through DTC, you should have received a voting instruction card and voting instructions with these proxy materials from that organization rather than from us. Simply complete and mail the voting instruction card to ensure that your vote is counted, or follow such instructions to submit your vote by the internet or telephone, if the instructions provide for internet and telephone voting. To vote in person at the Annual Meeting, you must obtain a valid proxy from your broker, bank, or other agent. Follow the instructions from your broker, bank, or other agent included with these proxy materials, or contact your broker, bank, or other agent to request a proxy form.


4.			Who counts the votes?

Broadridge Financial Solutions, Inc. (“Broadridge”) has been engaged as our independent agent to tabulate shareholder votes.


5.			How are votes counted?

With respect to each of Proposal Nos. 1, 2, and 3, an affirmative vote of a simple majority of the votes cast in person or by proxy at the Annual Meeting is required for approval.

If your shares are held by a broker on your behalf (that is, in “street name”), please instruct your broker on how to vote your shares. If you do not provide voting instructions, your shares will not be voted on any proposal for which the broker does not have discretionary authority to vote. This is called a “broker non-vote.” In these cases, the broker can register your shares as being present at the Annual Meeting for purposes of determining the presence of a quorum, and exercise its discretionary authority to vote on Proposal 2, but will not be able to vote on those proposals for which specific authorization from you is required under applicable rules. Accordingly, while broker non-votes will not be counted as having been voted on a particular proposal, broker non-votes will be considered present and entitled to vote at the

Annual Meeting and will be counted toward determining whether or not a quorum is present. We strongly encourage you to provide voting instructions to your broker to ensure that your vote is counted on all of the proposals.

If shareholders abstain from voting, including brokers holding their clients’ shares of record who cause abstentions to be recorded, these shares will be considered present and entitled to vote at the Annual Meeting and will be counted toward determining whether or not a quorum is present. Abstentions will not, however, be considered votes cast at the Annual Meeting.

Because the approval of each of the proposals is based on the votes cast at the Annual Meeting, abstentions and broker non-votes will not have any effect on the outcome of voting on any of the proposals.


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THE PROXY PROCESS AND SHAREHOLDER VOTING
QUESTIONS AND ANSWERS ABOUT THESE PROXY MATERIALS AND VOTING


6.			How many votes do I have?

On each matter to be voted upon, you have one vote for each ordinary share you own as of the Record Date.


7.			Why did I receive a notice in the mail regarding the internet availability of proxy materials instead of a full set of proxy materials?

Pursuant to rules of the U.S. Securities and Exchange Commission (the “SEC”), Irish law, and our Constitution, we have elected to provide access to our proxy materials on the internet. Accordingly, we are sending a Notice of Internet Availability of Proxy Materials to our shareholders. All shareholders will have the ability to access the proxy materials on the website referred to in the Notice of Internet Availability of Proxy Materials or request to receive a printed set of the proxy materials. Instructions on

how to access the proxy materials on the internet or to request a printed copy may be found in the Notice of Internet Availability of Proxy Materials. In addition, shareholders may request to receive proxy materials in printed form by mail or electronically by email on an ongoing basis. We encourage shareholders to take advantage of the availability of the proxy materials on the internet to help reduce the environmental impact of the Annual Meeting.


8.			How do I vote via internet or telephone?

You may vote by proxy on the internet by following the instructions provided on the proxy card or in the Notice of Internet Availability of Proxy Materials. If you request printed copies of the proxy materials by mail, you may vote by proxy by calling the toll-free number found on the proxy card. Please be aware that if you vote on the internet, you may incur costs such as internet access or telephone charges for which you will be responsible. The internet and telephone voting facilities for eligible shareholders of record will close at 11:59 p.m. Eastern Time on May 13, 2026. The giving of such a proxy by internet

or telephone will not affect your right to vote in person should you decide to attend the Annual Meeting.

The internet and telephone voting procedures are designed to authenticate shareholders’ identities, to allow shareholders to give their voting instructions and to confirm that shareholders’ instructions have been recorded properly. If you vote by internet or telephone, that vote authorizes your proxy in the same manner as if you signed, dated, and returned a written proxy card by mail.


9.			What if I return a proxy card but do not make specific choices?

If we receive a signed and dated proxy card and the proxy card does not specify how your shares are to be voted, your shares will be voted as follows:

•FOR the election, by separate resolutions, of Mr. Cooke and Dr. Selkoe, as directors, to hold office until no later than our annual general meeting of shareholders in 2029;

•FOR the ratification, in a non-binding vote, of the appointment of KPMG LLP as our independent registered public accounting firm for our fiscal year 2026 and authorization, in a binding vote, of our Board, acting through its Audit Committee, to approve the remuneration of that auditor; and

•FOR the approval, in a non-binding advisory vote, of the compensation of our named executive officers.

If any other matter is properly presented at the Annual Meeting, your proxy (one of the individuals named on your proxy card) will vote your shares using his or her discretion.


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			THE PROXY PROCESS AND SHAREHOLDER VOTING
QUESTIONS AND ANSWERS ABOUT THESE PROXY MATERIALS AND VOTING


10.			Who is paying for this proxy solicitation?

We will pay for the entire cost of soliciting proxies. In addition to these mailed proxy materials, our directors, officers, and employees may also solicit proxies in person, by telephone, or by other means of communication. Directors, officers, and employees will not be paid any additional compensation for soliciting proxies. We may also reimburse brokerage

firms, banks, and other agents for the cost of forwarding proxy materials to beneficial owners. In addition, we have retained Alliance Advisors, a proxy solicitation firm, to assist in the solicitation of proxies for a fee of approximately $20,000, plus reimbursement of expenses.


11.			What does it mean if I receive more than one set of materials?

If you receive more than one set of materials, your shares are registered in more than one name or are registered in different accounts. In order to vote all the shares you own, you must either sign and return

all of the proxy cards or follow the instructions for any alternative voting procedure on each of the proxy cards or Notice of Internet Availability of Proxy Materials you receive.


12.			Can I change my vote after submitting my proxy?

Yes. You may revoke your proxy at any time before commencement of the Annual Meeting. If you are the record holder of your shares, you may revoke your proxy in any one of three ways:

•You may submit a new vote on the internet or by telephone or submit another properly completed proxy card with a later date than your original proxy card, but no later than 11:59 p.m. Eastern Time on May 13, 2026.

•You may deliver a written notice that you are revoking your proxy to our Company Secretary at Prothena Corporation plc, 77 Sir John Rogerson’s

Quay, Block C, Grand Canal Docklands, Dublin 2, D02 VK60, Ireland, which notice must be delivered no later than 11:59 p.m. Eastern Time on May 13, 2026.

•You may attend the Annual Meeting and either vote or revoke your proxy in person. Simply attending the Annual Meeting will not, by itself, revoke your proxy.

If your shares are held by your broker, bank, or other agent, you must contact the broker, bank, or other agent and follow the instructions provided by them.


13.			When are shareholder proposals and nominations due for next year's annual meeting?

In accordance with Rule 14a-8 of the Securities Exchange Act of 1934, as amended (the "Exchange Act"), shareholders may submit to us proposals on matters appropriate for shareholder action at meetings of our shareholders. In order to be considered for inclusion in next year's proxy materials, your proposal must comply with the requirements of Rule 14a-8 of the Exchange Act and other SEC rules and be submitted in writing no later than November 27, 2026, to our Company Secretary at Prothena Corporation plc, 77 Sir John Rogerson’s Quay, Block C, Grand Canal Docklands, Dublin 2, D02 VK60, Ireland; provided that if the date of next year's annual general meeting of shareholders is greater than 30 days from May 14, 2027, the deadline is a reasonable time before we begin to print and send our proxy materials for next year’s annual general meeting.

For a shareholder to make any formal nomination of a director candidate for election to the Board at the 2027 annual general meeting of shareholders, the shareholder must provide notice to the Company not earlier than October 28, 2026, and not later than December 27, 2026, and must otherwise comply with the requirements set forth in our Constitution. You are advised to review our Constitution, which contains additional requirements about advance notice of director nominations. For more information, see below under the heading Corporate Governance and Board Matters - Board Committees - Nominating and Corporate Governance Committee.

In addition to satisfying the requirements regarding director nominations in our Constitution, to comply with the universal proxy rules, shareholders who intend to solicit proxies in support of director


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THE PROXY PROCESS AND SHAREHOLDER VOTING
QUESTIONS AND ANSWERS ABOUT THESE PROXY MATERIALS AND VOTING

nominees other than the Company’s nominees must provide notice that sets forth the information required

by Rule 14a-19 under the Exchange Act no later than March 15, 2027.


14.			What is the quorum requirement?

A quorum of shareholders is necessary to hold a valid meeting. A quorum will be present if the holders of not less than one-half of the ordinary shares issued and outstanding and entitled to vote are present in person or represented by proxy at the Annual Meeting. On the Record Date, there were 53,832,982 ordinary shares issued and outstanding and entitled to vote. Accordingly, 26,916,491 ordinary shares must be represented in person or by proxy at the Annual Meeting to have a quorum.

Your shares will be counted toward the quorum if you submit a valid proxy vote or vote at the Annual Meeting. Abstentions and broker non-votes will also be counted toward the quorum requirement. If there is no quorum, either the chairperson of the Annual Meeting or a majority in voting power of the shareholders entitled to vote at the Annual Meeting, present in person or represented by proxy, may adjourn the Annual Meeting to another time or place.


15.			How can I find out the results of the voting at the Annual Meeting?

Voting results will be announced by the filing with the SEC of a Current Report on Form 8-K within four business days after the Annual Meeting.


16.			Where can I find directions to the Annual Meeting?

To obtain directions to the Annual Meeting, which will be held at The Merrion Hotel, Upper Merrion Street, Dublin 2, D02 KF79, Ireland, you may send a request

to our Company Secretary at Prothena Corporation plc, 77 Sir John Rogerson’s Quay, Block C, Grand Canal Docklands, Dublin 2, D02 VK60, Ireland.


17.			What are the Irish statutory financial statements?

Since we are an Irish company, we are required to prepare Irish statutory financial statements, including the respective reports of the directors and the auditors thereon, under applicable Irish company law; to deliver those statutory financial statements to our shareholders of record prior to the Annual Meeting; and to present those statutory financial statements at the Annual Meeting. The Irish statutory financial statements cover the results of operations and financial position of the Company for our fiscal year 2025, and are prepared in accordance with generally accepted accounting principles in the United States to the extent the use of such principles does not contravene any provision of the Irish Companies Act 2014 or any regulation thereunder.

There is no requirement under Irish law that our Irish statutory financial statements be approved by our shareholders and no such approval will be sought at the Annual Meeting. Our Irish statutory financial statements are available on our website at https://ir.prothena.com/investors/financials-filings/Irish-Statutory-Financial-Statements/. We will mail without charge, upon written request, a copy of our Irish statutory financial statements to beneficial owners of our shares. Such requests should be sent to our Company Secretary at Prothena Corporation plc, 77 Sir John Rogerson’s Quay, Block C, Grand Canal Docklands, Dublin 2, D02 VK60, Ireland.


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PROPOSAL NO. 1			ELECTION OF DIRECTORS


Summary

The Company’s Constitution requires that at least one-third (which, if not a round number, is rounded to the number which is nearest to and less than one-third) of the directors (excluding any director who wishes to retire and does not wish to offer themselves for re-appointment, and any director appointed by the Board to fill a vacancy since the last annual general meeting) must stand for election at each annual general meeting of shareholders, and that directors must stand for election no later than the third annual general meeting subsequent to their election or appointment to the Board. Generally, vacancies on the Board may be filled only by ordinary resolution of the Company’s shareholders or the affirmative vote of a majority of the remaining directors. A director appointed by the Board to fill a vacancy will serve until the subsequent annual general meeting and must stand for election at that time.

As of the date of this Proxy Statement, we have eight directors serving on our Board. Helen S. Kim, whose current term will expire at the Annual Meeting, is not standing for election at the Annual Meeting. Our Board plans to reduce its size to seven members immediately following the Annual Meeting. Our Board currently is divided into the following groups:

•Helen S. Kim and Dennis J. Selkoe, whose current terms will expire at the Annual Meeting;

•Richard T. Collier, Shane M. Cooke, William H. Dunn, Jr., and Daniel G. Welch, whose current terms will expire no later than the annual general meeting of shareholders to be held in 2027; and

•Lars G. Ekman and Gene G. Kinney, whose current terms will expire no later than the annual general meeting of shareholders to be held in 2028.

Mr. Cooke and Dr. Selkoe have been nominated by the Board to stand for election. Each of Mr. Cooke and Dr. Selkoe were previously elected to the Board by our shareholders. The Board nominated Mr. Cooke to stand for election even though his three-year term does not expire until 2027 because the Company’s Constitution requires that one-third of the directors (excluding any director who wishes to retire and does not wish to offer themselves for re-appointment, and any director appointed by the Board to fill a vacancy since the last annual general meeting) stand for election at each annual general meeting and that a director longest in office since being appointed or last elected must be nominated to complete such slate of directors. If elected by our shareholders at the Annual Meeting, Mr. Cooke and Dr. Selkoe will each hold office from the date of their election until no later than the third subsequent annual general meeting of shareholders (i.e., in 2029), or until their earlier death, resignation, or removal.

In order to be elected as a director, each nominee must receive the affirmative vote of a majority of the votes cast in person or by proxy at the Annual Meeting; if a director nominee does not receive this majority vote, such nominee will not be elected to the Board. In the event that any nominee becomes unavailable for election as a result of an unexpected occurrence, the proxy holders may vote your shares for the election of any substitute nominee whom the Board proposes. Each person nominated for election has consented to being named as a nominee in this Proxy Statement and agreed to serve if elected, and management has no reason to believe that any nominee will be unable to serve.


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PROPOSAL NO. 1 – ELECTION OF DIRECTORS

The table below is provided to highlight the specific skills, qualifications, and other attributes of our director nominees and continuing directors. The lack of a mark for a particular item for a particular director does not mean the director lacks that skill or qualification; rather, a mark indicates a specific area of focus or expertise for which the Board relies on such director most. Also provided are summary statistics regarding the composition of the Board.

Following the table below is certain biographical information for each nominee for director and each director whose term as a director will continue after the Annual Meeting, which includes information regarding each person’s individual experience, qualifications, attributes, or skills that led the Board to conclude that such person should serve as a director, in light of our business and structure.

Skills and Qualifications

Richard T. Collier

Shane M. Cooke

William H. Dunn, Jr.

Lars G. Ekman

Gene G. Kinney

Dennis J. Selkoe

Daniel G. Welch

Science & Research

Scientific expertise in biopharmaceutical research and/or in relevant medical fields

Clinical Development and Operations

Experience in the design and implementation of clinical studies in support of drug development

Regulatory

Experience with regulation in the healthcare industry

Drug Commercialization

Experience with bringing drugs to market

Business Strategy/Operations

Experience overseeing and driving strategic direction and growth of an organization

Finance/Accounting

Experience or expertise in financial accounting and reporting processes or the financial management of an organization

Legal/Ethics/Public Policy

Experience with legal and ethical and public policy issues in the healthcare industry

Public Company Governance

Service on a public company board other than Prothena’s

Capital Markets & M&A Experience

Experience in capital market transactions or mergers and acquisitions

Human Capital Management

Experience in attracting and retaining top talent and building organizational culture


Basic Information (as of 3/27/2026)	Richard T. Collier	Shane M. Cooke	William H. Dunn, Jr.	Lars G. Ekman	Gene G. Kinney	Dennis J. Selkoe	Daniel G. Welch
Independent	l	l	l	l		l	l
Age	72	63	56	76	57	82	68
Tenure (Years)	13.3	13.3	2.9	13.3	9.5	12.7	2.1


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PROPOSAL NO. 1 – ELECTION OF DIRECTORS


Nominees for Election to Terms Expiring No Later than the Annual General Meeting of Shareholders in 2029; Recommendation of the Board

Shane M. Cooke is the former President of Alkermes plc (a biopharmaceutical company), a position he held from 2011 to 2018. Prior to that, he served as Head of Elan Drug Technologies and Executive Vice President of Elan Corporation, plc (from 2007 to 2011), where he also served as Chief Financial Officer (from 2001 to 2011) and as a director (from 2005 to 2011). Mr. Cooke has also held a number of senior positions in finance in the banking and aviation industries. He is a director of Alkermes plc (a biopharmaceutical company whose board he joined in 2018), and served as a director of Endo International plc (a biopharmaceutical company) (from 2014 to April 2024), and as a director (from 2019 to 2020) and chair of the board (from 2020 until its acquisition by Clayton, Dubilier & Rice, LLC in 2021) of UDG Healthcare plc (a pharmaceutical services company). Mr. Cooke earned his Bachelor of Commerce and Master of Accounting degrees from University College Dublin, Ireland, and is a chartered accountant. He has served on our Board since 2012. Age: 63

The Board concluded that Mr. Cooke should continue to serve as a director given his significant operational, financial, commercial, and management experience in the biotechnology industry, as well as his qualification as a chartered accountant. The Board also considered his Irish residency and experience as a director and an executive officer of other Irish companies traded on U.S. stock exchanges.

Dennis J. Selkoe, M.D., is the Vincent and Stella Coates Professor of Neurologic Diseases at Harvard Medical School and co-director of the Ann Romney Center for Neurologic Diseases at Brigham and

Women's Hospital in Boston, positions he has held since 2000 and 1985, respectively. He has served on the faculty at Harvard Medical School since 1978. Dr. Selkoe was the principal founding scientist and served as a director of Athena Neurosciences, Inc. until it was acquired by Elan Corporation, plc in 1996. He has received numerous honors, including the Mathilde Solowey Award in the Neurosciences (NIH), the Potamkin Prize (American Academy of Neurology), the A.H. Heineken Prize for Medicine (The Netherlands), the Pioneer Award and the Lifetime Achievement Award (Alzheimer's Association), the George C. Cotzias Lecture of the American Academy of Neurology, and the Ulysses Medal of University College Dublin. Dr. Selkoe is a Fellow of the American Academy of Neurology, the American Association for the Advancement of Science and the American College of Physicians, an elected member of the National Academy of Medicine and a director of the Foundation for Neurologic Diseases. He served as a director of Elan Corporation, plc from 1996 to 2013. Dr. Selkoe earned his B.A. from Columbia University and his M.D. from the University of Virginia. He has served on our Board since 2013. Age: 82

The Board concluded that Dr. Selkoe should continue to serve as a director given his significant experience as both a research scientist and a practicing clinician, and in particular his expertise in the preclinical and clinical features of neurodegenerative diseases, especially Parkinson's disease and Alzheimer's disease. The Board also considered his lengthy experience as a director of a global public company in the pharmaceutical/biotechnology industry.


THE BOARD OF DIRECTORS UNANIMOUSLY RECOMMENDS THAT SHAREHOLDERS VOTE FOR THE ELECTION, BY SEPARATE RESOLUTIONS, OF MR. COOKE AND DR. SELKOE AS DIRECTORS.


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Directors Continuing in Office Until No Later than the Annual General Meeting of Shareholders in 2027

Richard T. Collier is the former Executive Vice President and General Counsel of Elan Corporation, plc, a position he held from 2004 to 2010. Prior to that, he served as Senior Vice President and General Counsel of Rhone-Poulenc Rorer Inc., Pharmacia & Upjohn Company, and Pharmacia Corporation. Mr. Collier was an Adjunct Professor of Law at the Temple University Beasley School of Law, where he taught drug and medical device law, from 2004 to 2017. He also practiced law at two leading Philadelphia-based law firms and with the U.S. Federal Trade Commission and U.S. Department of Justice. Mr. Collier earned both his B.A. and his J.D. from Temple University. He has served on our Board since 2012. Age: 72

The Board concluded that Mr. Collier should continue to serve as a director given his extensive legal and management experience as a senior executive with a number of global pharmaceutical companies. The Board also considered his extensive knowledge of and experience with laws and regulations applicable to the pharmaceutical industry.

William H. Dunn, Jr., M.D., was the founding director of the Office of Neuroscience, Center for Drug Evaluation and Research, at the U.S. Food and Drug Administration, a position he held since the founding of the office in 2019 through February 2023. He was responsible for the regulatory oversight of all research conducted to support neuroscience drug development, including the regulation and review of investigational new drug applications and marketing applications for drug and biologic products. From 2005 to 2019, he held positions of increasing seniority in the Division of Neurology Products, Center for Drug Evaluation and Research, including his role as director of that division. Dr. Dunn is a trained neurologist and vascular neurologist with experience in basic research, clinical research, and clinical care. He earned his B.A. from the University of Virginia and his M.D. from the F. Edward Hébert School of Medicine in Bethesda, Maryland. He has served on our Board since 2023. Age: 56

The Board concluded that Dr. Dunn should continue to serve as a director given his significant regulatory experience with the U.S. FDA and experience in the design and implementation of clinical studies in support of drug development. The Board also considered his scientific and medical expertise in the neurodegenerative field, and operational experience in a large organization.

Daniel G. Welch serves as the chair of the boards of Structure Therapeutics Inc. (since January 2022) and Ultragenyx Pharmaceuticals Inc. (since 2015). He previously served as chair of the board of Nuvation Bio Inc. (from 2020 to September 2024), as a director of SeaGen Inc. (from 2007 until its acquisition by Pfizer in 2023), as chair of the board of AveXis Inc (from 2016 until its acquisition by Novartis in 2018), as a director of Intercept Pharmaceuticals, Inc. (from 2015 to 2020), and as a director of Hyperion Therapeutics (from 2012 until its acquisition by Horizon Pharma in 2015). Prior to these roles he served as an executive partner at Sofinnova Ventures (from 2015 to 2018), as Chief Executive Officer and President of InterMune, Inc. (from 2003 until its acquisition by Roche Holdings in 2014), as chair of the board of InterMune (from 2008 to 2014), as chair of the board and Chief Executive Officer of Triangle Pharmaceuticals, Inc. (from 2002 until its acquisition by Gilead Sciences in 2003), and as President of the pharmaceutical division of Elan Corporation, plc (from 2000 to 2002). Mr. Welch earned his B.A. from the University of Miami and his M.B.A. from the University of North Carolina. He has served on our Board since February 2024 and as Chair of our Board since May 2024. Age: 68

The Board concluded that Mr. Welch should continue to serve as a director given his significant experience serving on the boards of public companies in the pharmaceutical/biotechnology industry. The Board also considered his experience in executive management at several publicly-traded companies in the pharmaceutical/biotechnology industry.


Directors Continuing in Office Until No Later than the Annual General Meeting of Shareholders in 2028

Lars G. Ekman, M.D., Ph.D., is an executive partner at Sofinnova Ventures, Inc. (a venture capital firm), a position he has held since 2008. Dr. Ekman served as a director of Ultragenyx Pharmaceutical Inc. (from 2016 to June 2023), as a director and then chair of the board of Amarin Corporation plc (from 2008 to 2022), as a director of Intermune Inc. (from 2006 to 2013), as a director of Ocera Therapeutics, Inc. (from 2009 to 2015), as a director of Spark Therapeutics, Inc. (from 2014 to 2019), and as Chair of the Board

of Sophiris Bio Inc. (from 2010 to 2020). Dr. Ekman co-founded Cebix Incorporated, where he served as Chief Executive Officer from 2009 to 2012. He was President of Research & Development at Elan Corporation, plc (from 2001 to 2007), where he also served as a director (from 2005 to 2012). From 1997 to 2001, Dr. Ekman was Executive Vice President, Research & Development, at Schwarz Pharma AG. Prior to that, he held various senior positions at Pharmacia Corporation. Dr. Ekman is a board-certified


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surgeon with a Ph.D. in experimental biology and has held several clinical and academic positions in both the United States and Europe. He earned his Ph.D. and M.D. from the University of Gothenburg, Sweden. Dr. Ekman has served on our Board since 2012 and served as Chair of our Board from 2012 until May 2024. Age: 76

The Board concluded that Dr. Ekman should continue to serve as a director given his significant scientific, operational, and management experience gained as a research scientist and in managing research and development functions engaged in drug discovery with a number of companies in the pharmaceutical industry. The Board also considered his clinical background, his venture capital experience in the life science industry, and his experience serving on the boards of directors at a number of public and private companies in the pharmaceutical/biotechnology industry.

Gene G. Kinney, Ph.D., has served as our President and Chief Executive Officer since 2016. Prior to that, he was our Chief Operating Officer for part of 2016, and prior to that he was our Chief Scientific Officer and Head of Research and Development from 2012 to 2016. From 2009 to 2012, Dr. Kinney held various positions with Elan Pharmaceuticals, Inc.: Vice President, Pharmacology (from 2011 to 2012) and Senior Vice President of Pharmacological Sciences (from 2009 to 2011); and while in those positions, he also served as Head of Nonclinical Research for Janssen Alzheimer Immunotherapy R&D. From 2001 to 2009, Dr. Kinney was Senior Director, Head of Central Pharmacology and acting lead for Bioanalytics & Pathology at the Merck Research Laboratories, where he contributed to the strategic direction and oversight of drug discovery activities and led a number of non-clinical discovery and clinical development programs targeted for the treatment of neurodegenerative and psychiatric conditions. Dr. Kinney also held positions at Bristol Myers Squibb and was an Assistant Professor at the Emory University School of Medicine, Department of Psychiatry and Behavioral Sciences. He earned his B.A. from Bloomsburg University and his M.A. and Ph.D. from Florida Atlantic University. Dr. Kinney has served on our Board since 2016. Age: 57

The Board concluded that Dr. Kinney should continue to serve as a director given his role as the Company’s President and Chief Executive Officer and his extensive scientific and operational knowledge of our business and its drug discovery and development programs, from his tenure with the Prothena business when it was a part of Elan as well as since its separation from Elan. The Board also considered his significant experience in neuroscience and drug development programs encompassing immunotherapy, vaccine and small molecule approaches, as well as his experience gained from serving in key research and development leadership roles in other biotechnology companies.


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CORPORATE GOVERNANCE AND BOARD MATTERS


Overview

We are committed to exercising good corporate governance practices. In furtherance of this commitment, we regularly monitor developments in the area of corporate governance and review our processes, policies, and procedures in light of such developments. Key information regarding our corporate governance can be found on our website at https://ir.prothena.com/corporate-governance, including in our Corporate Governance Guidelines; the

charters for our Audit, Compensation, Nominating and Corporate Governance, and Research and Development Committees; and our Code of Conduct. We believe that our corporate governance policies and practices are adequately designed to ensure that our independent directors effectively oversee our management - including the performance of our Chief Executive Officer - and provide an effective and appropriately balanced Board governance structure.


Independence of Directors

Rules of The Nasdaq Stock Market ("Nasdaq") require that a majority of the members of a listed company’s board of directors must qualify as "independent directors" as defined by Nasdaq rules and affirmatively determined by the board of directors.

Our Board has determined that, with the exception of Dr. Kinney, all members of our Board (including

Paula K. Cobb, who served on our Board during 2025) qualify as "independent directors" as defined by Nasdaq rules. Dr. Kinney is not an independent director because he is our President and Chief Executive Officer.


Board Role in Risk Oversight

Our Board is responsible for the oversight of risk, while management is responsible for the day-to-day management of risk. The Board fulfills this oversight role directly and through certain of its committees as described in more detail below and in the respective charters of each committee. In particular, our Board reviews strategic as well as operational risks as an element of its review of strategic and operational plans and programs.

The Audit Committee of the Board periodically reviews the Company’s major risk exposures and the steps management has undertaken to control them; oversees internal controls and other activities to manage financial risks; and periodically reviews the Company’s policies, programs, and systems intended to ensure compliance with applicable laws and ethical standards.


Board Leadership Structure

Our Chair of the Board and our Chief Executive Officer are currently separate individuals. Mr. Welch serves as Chair of the Board, and Dr. Kinney serves as our President and Chief Executive Officer. In his role as Chair, Mr. Welch provides leadership to the Board; approves Board meeting schedules and agendas; presides over all Board meetings, including regular executive sessions of the independent directors; and serves as the primary liaison between the independent directors and our Chief Executive Officer and other members of management.

Since Mr. Welch’s appointment as Chair of the Board in May 2024, Dr. Ekman, who had served as Chair of our Board since 2012, has served as Chair Emeritus. Our Board has concluded that the proposed leadership structure is appropriate at this time. However, our Board will continue to periodically review our leadership structure and may make changes as it deems appropriate.


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Board Committees

Our Board has the following standing committees: the Audit Committee, the Compensation Committee, the Nominating and Corporate Governance Committee, and the Research and Development Committee. Each of these committees operates under a written charter which sets forth the functions and responsibilities of the committee, a copy of which is available on our

website at https://ir.prothena.com/corporate-governance. The current composition and responsibilities of each of these committees are described below. Members serve on these committees until their resignation or until otherwise determined by our Board.

Director

Audit
Committee

Compensation
Committee

Nominating and
Corporate Governance
Committee

Research and Development Committee

Richard T. Collier

SEC Form DEF 14A filed by Prothena Corporation plc